Flat flow gasification furnace coupling coal powder boiler system's steady combustion control method

Abstract

The present application relates to the technical field of pulverized coal boiler control, and discloses a stable combustion control method of a flat plug flow gasification furnace coupled with a pulverized coal boiler system, which comprises the following steps: determining whether the target load in the boiler load reduction instruction of the pulverized coal boiler belongs to an ultra-low load; when the target load is less than 35% BMCR, S1, first reducing the boiler load of the pulverized coal boiler to 35% BMCR according to the load adjustment method when the boiler is operated under normal load, then switching the coal powder feeding of the boiler burner to the flat plug flow gasification furnace, increasing the supplementary combustion air, and operating for 10-30 minutes; S2, monitoring the combustion zone temperature and determining whether the pulverized coal boiler is stably combusted; when the monitored combustion zone temperature is higher than the minimum stable combustion temperature and the outlet temperature of the gasification furnace is greater than 1000 DEG C, the coal feeding amount of the gasification furnace, the inlet air amount of the gasification furnace and the supplementary combustion air amount of the boiler combustion zone are adjusted in real time until the target load is reduced. The method provided by the present application realizes the coordination and high efficiency of the two devices and ensures that the pulverized coal boiler can be safely and stably combusted under an ultra-low load.

Description

Technical Field

[0001] This invention relates to the field of pulverized coal boiler control technology, specifically to a stable combustion control method for a push flow gasifier coupled with a pulverized coal boiler system. Background Technology

[0002] Against the backdrop and trend of reducing carbon emissions, the power grid system has placed higher demands on the deep peak shaving of renewable energy. In specific environments, pulverized coal boilers need to operate under ultra-low loads to meet the needs of renewable energy grid connection. Ensuring the safe and stable combustion of pulverized coal boilers under ultra-low loads presents a serious technical challenge.

[0003] The current main method involves adding oil burners, similar to continuous lamps, to the existing pulverized coal boiler. By increasing the load on the oil burners under ultra-low load conditions, the combustion stability of the pulverized coal boiler system is ensured. This technical solution has played a good role in ensuring the stable and safe operation of the system. However, due to the high price of oil and the complexity of the system, it significantly increases the operating costs of the power plant. Therefore, developing an economically feasible ultra-low load stable combustion technology for pulverized coal boilers using the power plant's inherent resources is particularly important.

[0004] CN108518666 A describes a stable combustion system and method for a pulverized coal boiler using coal as fuel. The system includes a gasifier body, a pulverized coal boiler, and a first steam drum. The gasifier body is a vertical gasifier, divided from top to bottom into a gasification section, a radiant waste boiler section, and an ash pool section. The syngas produced by gasification is transported through a pipeline from the bottom of the gasifier to the pulverized coal boiler for combustion support. The gasification ash is post-processed using conventional gasification methods. This patent merely provides a rigid connection between the gasifier and the pulverized coal boiler; the syngas produced by gasification is used for combustion support in the pulverized coal boiler under low load, similar to the independent operation of two separate systems. Furthermore, it does not disclose its stable combustion control method, which may lead to energy waste in actual operation.

[0005] CN207674428 U describes a coal-fired power unit coupled with biomass gasification power generation and gas combustion system. The system includes a circulating fluidized bed, separation equipment, heat exchanger, and pressurization equipment. The patent describes how syngas is produced by gasifying in a circulating fluidized bed and then undergoing a series of post-processing steps to replace the existing petroleum-assisted combustion system, thereby ensuring stable combustion of the system.

[0006] CN104848248 B introduces a coal-fired combustion air distribution control technology for boilers in thermal power plants that burn pulverized coal, blast furnace gas, and coke oven gas. This patent primarily calculates the required energy based on the boiler's evaporation rate, then calculates the energy that can be generated based on the calorific value and flow rate of fuel oil, blast furnace gas, and coke oven gas. Next, it subtracts the energy generated by blast furnace gas and coke oven gas from the energy required by the boiler load to calculate the energy generated by the pulverized coal. Then, it calculates the calorific value of the pulverized coal based on the total coal quantity in the coal mill and the required energy generated by the pulverized coal. Finally, it controls the opening of the dampers on each layer of the coal mill based on the calculated calorific value and the output of each layer of the coal mill. This patent's technical solution mainly describes the existing conversion methods for blast furnace gas and coke oven gas, but there are significant differences in the calorific value conversion methods for gasifiers. This technical solution cannot be directly transferred to the conversion of pulverized coal and gasifying agent in gasifiers.

[0007] Therefore, there is an urgent need to provide a stable combustion control method for pulverized coal boilers under ultra-low loads. Summary of the Invention

[0008] The purpose of this invention is to overcome the problem of poor safety of pulverized coal boilers under ultra-low load in the prior art, and to provide a stable combustion control method for a push flow gasifier coupled with a pulverized coal boiler system.

[0009] To achieve the above objectives, the present invention provides a combustion stabilization control method for a push-flow gasifier coupled with a pulverized coal boiler system, the method comprising the following steps:

[0010] Determine whether the target load in the boiler load reduction instruction of the pulverized coal boiler belongs to the ultra-low load; wherein, when the target load is <35%BMCR, the target load is the ultra-low load;

[0011] When the target load is not an ultra-low load, the horizontally installed pusher gasifier is used as the primary air duct, and the load is adjusted according to the load adjustment method of the pulverized coal boiler under normal load.

[0012] When the target load is an ultra-low load:

[0013] S1. First, reduce the boiler load of the pulverized coal boiler to 35% BMCR according to the load adjustment method when the boiler is running under normal load. Then, switch the pulverized coal feed from the boiler burner to the pusher flow gasifier and increase the supplementary combustion air. Run for 10-30 minutes.

[0014] S2, monitor the temperature in the combustion zone to determine whether the minimum stable combustion temperature and the gasifier outlet temperature meet the conditions for stable combustion in the pulverized coal boiler.

[0015] When the temperature of the combustion zone is lower than the minimum stable combustion temperature, or the gasifier outlet temperature is less than 1000℃, it indicates that the boiler combustion is unstable. Increase the coal feed rate of the gasifier, keep the primary air volume of the gasifier constant, increase the inlet air volume of the gasifier, and reduce the supplementary combustion air volume of the boiler until the combustion is stable.

[0016] When the temperature of the combustion zone is higher than the minimum stable combustion temperature and the gasifier outlet temperature is greater than 1000℃, it indicates that the boiler combustion is stable. Keep the steam superheater outlet temperature unchanged, and adjust the coal feed rate of the gasifier, the air flow rate at the gasifier inlet, and the supplementary combustion air flow rate in the boiler combustion zone in real time until the pulverized coal boiler load is reduced to the target load.

[0017] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0018] (1) The stable combustion control method of the push-flow gasifier coupled with the pulverized coal boiler system provided by the present invention is that the push-flow gasifier is placed horizontally so that the flow direction of the gasifier outlet and the flow direction of the unreacted powder are consistent with the direction of the pulverized coal and the primary air entering the boiler. This can transport all the high-temperature syngas (CO, CH4, H2, tar, etc.) generated by the gasifier and the incompletely gasified pulverized coal into the pulverized coal boiler under pressure, thereby improving the utilization rate of pulverized coal and reducing the complexity of the modification.

[0019] (2) The present invention provides a stable combustion control method for a pusher flow gasifier coupled with a pulverized coal boiler system. This method relies on the pusher flow gasifier and the pulverized coal boiler coupling device to form a complete set of boiler ultra-low load combustion stable combustion control logic. It integrates the boiler conventional load adjustment and ultra-low load adjustment methods, controls the operation method and logic of the pusher flow gasifier in the ultra-low load adjustment process of the boiler, realizes the coordination and efficiency of the two devices, and ensures the stability of the entire system. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] This invention provides a method for stable combustion control of a push flow gasifier coupled with a pulverized coal boiler system, the method comprising the following steps:

[0022] Determine whether the target load in the boiler load reduction instruction of the pulverized coal boiler belongs to the ultra-low load; wherein, when the target load is <35%BMCR, the target load is the ultra-low load;

[0023] When the target load is not an ultra-low load, the horizontally installed pusher gasifier is used as the primary air duct, and the load is adjusted according to the load adjustment method of the pulverized coal boiler under normal load.

[0024] When the target load is an ultra-low load:

[0025] S1. First, reduce the boiler load of the pulverized coal boiler to 35% BMCR according to the load adjustment method when the boiler is running under normal load. Then, switch the pulverized coal feed from the boiler burner to the pusher flow gasifier and increase the supplementary combustion air. Run for 10-30 minutes.

[0026] S2, monitor the temperature in the combustion zone to determine whether the minimum stable combustion temperature and the gasifier outlet temperature meet the conditions for stable combustion in the pulverized coal boiler.

[0027] When the temperature of the combustion zone is lower than the minimum stable combustion temperature, or the gasifier outlet temperature is less than 1000℃, it indicates that the boiler combustion is unstable. Increase the coal feed rate of the gasifier, keep the primary air volume of the gasifier constant, increase the inlet air volume of the gasifier, and reduce the supplementary combustion air volume of the boiler until the combustion is stable.

[0028] When the temperature of the combustion zone is higher than the minimum stable combustion temperature and the gasifier outlet temperature is greater than 1000℃, it indicates that the boiler combustion is stable. Keep the steam superheater outlet temperature unchanged, and adjust the coal feed rate of the gasifier, the air flow rate at the gasifier inlet, and the supplementary combustion air flow rate in the boiler combustion zone in real time until the pulverized coal boiler load is reduced to the target load.

[0029] In this invention, BMCR refers to the maximum evaporation capacity of the boiler.

[0030] In a preferred embodiment, the method for adjusting the load according to the load adjustment method of the boiler under normal load includes: keeping the steam superheater outlet temperature constant, determining the load reduction rate k1, calculating the steam evaporation rate of the pulverized coal boiler using Formula 1 between the load reduction rate and the steam evaporation rate, calculating the coal feed rate of the pulverized coal boiler using Formula 2 between the steam evaporation rate and the coal feed rate, calculating the total air volume of the pulverized coal boiler using Formula 3 between the coal feed rate and the total air volume, calculating the primary air volume of the pulverized coal boiler using Formula 4 between the total air volume and the primary air volume, and adjusting the coal feed rate and the primary air volume of the pulverized coal boiler in real time according to the calculation results to reduce the load of the pulverized coal boiler to the target load;

[0031] M steam =M steam,0 -1146k1t Formula 1

[0032] In Equation 1, k1 is the load reduction rate, ranging from 1.2 to 2.4 tons per hour. 2 Msteam Steam evaporation rate, tons per hour, M steam，0 The steam evaporation rate of the boiler upon receiving the instruction is tons per hour; t is time, hours.

[0033] Q coal ×M coal ×θ=M steam ×[H P,T -H P1,T1 Formula 2 (b1)

[0034] In Equation 2, Q coal M is the calorific value of coal, expressed in kcal / kg. coal θ represents the coal feed rate in tons per hour; θ represents the boiler efficiency; P represents the steam pressure reference value in MPa; P1 represents the feedwater inlet pressure in MPa; T represents the steam temperature reference value in °C; T1 represents the feedwater inlet temperature in °C; where θ, P, P1, T, and T1 are determined by the pulverized coal boiler itself and are design parameters; H P,T H represents the enthalpy of superheated steam, expressed in kJ / kg. P1,T1 The enthalpy of the water supply is expressed in kJ / kg; H P,T and H P1,T1 The values ​​are taken from the corresponding temperature and pressure values ​​in the "Table of Enthalpy Values ​​of Water and Steam"; b1 is a correction coefficient, calculated using Equation 2 based on the design coal feed rate and design steam evaporation rate under BMCR conditions, that is...

[0035] F air =1.2f air ×M coal Formula 3

[0036] In Equation 3, F air Total air volume, Nm 3 / h; 1.2 is the excess air coefficient at the boiler furnace outlet, f air The amount of air required for the complete combustion of a unit mass of pulverized coal, in Nm³. 3 / ton; of which Nm 3 / ton represents the amount of air required for the complete combustion of one ton of pulverized coal, which can be determined through a test on the complete combustion of a unit mass of pulverized coal.

[0037] F air-1 =ηF air Formula 4

[0038] In Equation 4, F air-1 For primary air volume, Nm 3 / h; η is the proportion of primary air volume to total air volume, with a value range of 0.7-0.8.

[0039] In this invention, primary air volume refers to the air that transports pulverized coal through the burner into the furnace and supplies the oxygen required for the ignition and combustion of the volatiles in the pulverized coal. Other parameters during load adjustment, such as secondary air volume, are adjusted according to conventional methods in the art, and will not be elaborated upon here.

[0040] In a preferred embodiment, in S1, switching the pulverized coal feed from the boiler burner to the push-flow gasifier and increasing the supplementary combustion air specifically includes the following sub-steps:

[0041] S1-1, Calculate the pulverized coal boiler feed rate M when the boiler load drops to 35% BMCR using equations 1 to 4. coal35％ Total air volume F air35％ and primary air volume F (air-1)35％ ;

[0042] S1-2, the coal feed rate M of the pulverized coal boiler coal35％ Substitute the coal feed rate of the pulverized coal boiler and the coal feed rate of the gasifier into Equation 5 to calculate the coal feed rate of the gasifier.

[0043] That is to say

[0044] In Equation 5, M coal,1 The required coal feed rate for the gasifier, in tons per hour; This represents the heat loss of the gasifier, with a value ranging from 1% to 3%.

[0045] S1-3, Substitute the coal feed rate of the gasifier into Equations 3 and 4 to calculate the primary air volume of the gasifier. Nm 3 / h:

[0046] S1-4, Substitute the required coal feed rate of the gasifier into Equation 6 to calculate the inlet air volume of the gasifier:

[0047]

[0048] In Equation 6, The inlet air volume of the gasifier, Nm 3 / h;

[0049] S1-5, Substitute the primary air volume and gasifier inlet air volume of the gasifier into Equation 7 to calculate the supplementary combustion air volume in the boiler combustion zone:

[0050]

[0051] In Equation 7, The amount of supplemental combustion air for the boiler combustion zone, Nm 3 / h;

[0052] S1-6, adjust the coal feed rate of the gasifier, the air inlet rate of the gasifier, and the supplementary combustion air rate of the boiler combustion zone according to the calculation results, and run for 10-30 minutes.

[0053] In a preferred embodiment, S1 further includes adjusting the operation mode of the coal mill during the process of reducing the boiler load of the pulverized coal boiler to 35% BMCR, so that the average particle size of the pulverized coal exiting the mill is 50-100 μm, preferably 70-80 μm.

[0054] In a preferred embodiment, in step S2, the coal feed rate M of the pulverized coal boiler is... coal35％ and / or the primary air volume F of a pulverized coal boiler (air-1)35％ Substitute equations 8 and 9 to calculate the minimum stable combustion temperature at the boiler burner:

[0055]

[0056] That is to say

[0057] In Equation 8, q min The volumetric heat load at the boiler burner outlet, kJ / m³ 3 V represents the furnace volume at the boiler burner outlet, in meters. 3 ; 0.08 represents the proportion of the total heat released during coal combustion at the boiler burner;

[0058]

[0059] That is to say

[0060] In Equation 9, T feed,min Minimum stable ignition temperature, °C; T feed,0 The temperature at which fresh pulverized coal and air enter the boiler, in °C; c p,air is the specific heat value of air, kJ / (kg·K); c p,coal denoted as the average specific heat value of pulverized coal, in kJ / (kg·K).

[0061] If a temperature measuring device is used to measure the gasifier outlet temperature, the thermocouple may be damaged in a short time due to the scouring effect of the high-speed airflow and powder, resulting in inaccurate temperature readings. In a preferred embodiment, in step S2, the gasifier outlet temperature is calculated using the following formulas 10 to 21:

[0062] The chemical equation for the pyrolysis of pulverized coal in the gasifier is shown in Equation 10:

[0063]

[0064] In Equation 10, α2, α3, α4, α5 and α6 can be measured by analyzing the syngas produced after pyrolysis in the gasifier using a syngas component analyzer; coal char and moisture cannot be measured by the analyzer, but can be calculated based on the conservation of mass and matter.

[0065] The standard volume fractions of CO, H2, CH4, CO2, and N2 in the syngas can be obtained using a syngas component analyzer. The masses of CO, H2, CH4, CO2, and N2 in the syngas are m, ... CO m H2 m CH4 m CO2 m N2 The volume fraction can be calculated using the measured volume fraction and the constant n. Coal char is a solid and cannot be measured by the analyzer; moisture also cannot be measured by the analyzer, but it can be calculated based on the law of conservation of mass, as shown in Equation 11-18:

[0066] The constant n is calculated using the nitrogen mass conservation formula 11.

[0067]

[0068] In Equation 12-18, the mass flow rate of each component in the synthesis gas is calculated:

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076] In Formulas 11-18, α represents the mass percentage of dry-based carbon in pulverized coal, β represents the mass percentage of dry-based hydrogen in pulverized coal, γ represents the mass percentage of dry-based oxygen in pulverized coal, and δ represents the mass percentage of dry-based nitrogen in pulverized coal. The mass percentages of α, β, γ, and δ are determined by analytical laboratory testing according to national standard methods. The national standards used are GB / T212 Industrial Analysis Methods for Coal, GB / T213 Methods for Determination of Calorific Value of Coal, and GB / T 31391 Elemental Analysis Methods for Coal.

[0077] Substitute the calculation results from Equation 12-18 into Equation 19 to calculate the total flow rate of the syngas.

[0078]

[0079] In Equation 19, F syngas Syngas flow rate, Nm 3 / h;

[0080] The calorific value of syngas is calculated using Equation 20.

[0081]

[0082] In Equation 20, V H2 It is the molar proportion of H2 in the syngas (dry basis), V CH4 It is the molar proportion of CH4 in the syngas (dry basis), V CO It is the molar proportion of CO in the syngas (dry basis), F H2O It is the flow rate of water vapor in the syngas;

[0083] Calculate the gasifier outlet temperature T2 using Equation 21:

[0084]

[0085] In Equation 21, ΔH syngas The enthalpy of the synthesis gas at its minimum stable combustion temperature is given in kJ / m³. 3 ;c p,char The average specific heat value of semi-coke is equal to that of coal, expressed in kJ / (kg·K); m char The mass of semi-coke is expressed in kg / h; c p,air Specific heat of hot air, kJ / (kg·K); T air,2 The temperature of the supplemental combustion air in the combustion zone of the pulverized coal boiler, in °C; F* air The amount of supplemental combustion air for the combustion zone of a pulverized coal boiler, Nm 3 / h.

[0086] The enthalpy of syngas at its minimum stable combustion temperature is calculated using Equation 22.

[0087]

[0088] Using Dalton's law of partial pressures, the enthalpy of the syngas can be calculated based on the component content and enthalpy of each gas in the syngas. In Equation 22, ΔH i The enthalpy values ​​of the individual gases in the synthesis gas can be found in a common gas enthalpy-temperature table or calculated using process simulation software. The unit is kJ / Nm³. 3 ;F i For each gas, the flow rate is Nm. 3 / h.

[0089] When the gasifier outlet temperature is higher than 1000℃, it indicates that the gasifier is in normal working condition. If the gasifier outlet temperature is lower than 1000℃, it indicates that the gasification process is unstable and that the combustion zone temperature cannot be guaranteed to be higher than the minimum stable combustion temperature.

[0090] In a preferred embodiment, in step S2, when the temperature of the monitored combustion zone is lower than the minimum stable combustion temperature, or the gasifier outlet temperature is less than 1000°C, it indicates that the boiler combustion is unstable. The coal feed rate of the gasifier is increased by 3-8%, preferably 4-6%; the primary air volume of the gasifier is kept constant, and the inlet air volume of the gasifier is increased by 15-30%, preferably 20-25%, until the combustion is stable.

[0091] In a preferred embodiment, in step S2, the method for real-time adjustment of the coal feed rate of the gasifier, the inlet air rate of the gasifier, and the supplementary combustion air rate in the boiler combustion zone includes:

[0092] Keep the steam superheater outlet temperature constant, determine the load reduction rate k2, and calculate the steam evaporation rate using Equation 1; calculate the coal feed rate of the gasifier using Equations 2 and 5; calculate the primary air volume and gasifier inlet air volume of the gasifier using Equations 3, 4, and 6; calculate the supplementary combustion air volume of the boiler combustion zone using Equation 7; and adjust the coal feed rate, gasifier inlet air volume, and boiler combustion zone supplementary combustion air volume in real time according to the calculation results until the boiler load is reduced to the target load.

[0093] In a preferred embodiment, once the boiler load is reduced to the target load, the input values ​​of each parameter are maintained for stable operation.

[0094] In a preferred embodiment, during the real-time adjustment of the coal feed rate of the gasifier, the inlet air rate of the gasifier, and the supplementary combustion air rate in the boiler combustion zone, when a boiler malfunctions or a problem occurs with the pulverized coal, the pulverized coal boiler alarm sounds. At this time, the boiler combustion is unstable. The coal feed rate of the gasifier is increased, the primary air rate of the gasifier is kept constant, the inlet air rate of the gasifier is increased, and the supplementary combustion air rate in the boiler is decreased until the combustion is stable. Then, the coal feed rate of the gasifier, the inlet air rate of the gasifier, and the supplementary combustion air rate in the boiler combustion zone are adjusted in real time until the pulverized coal boiler load is reduced to the target load.

[0095] The present invention will be described in detail below through embodiments.

[0096] Example 1

[0097] The boiler used in Example 1 is a 300MW subcritical boiler. The boiler design parameters are: boiler efficiency θ = 92%, superheated steam pressure P = 17.5MPa, temperature T = 541℃, feedwater inlet pressure P1 = 17.7MPa, feedwater inlet temperature T1 = 241℃. According to the "Chart of Water and Steam Properties", the enthalpy H of the superheated steam is...P,T The enthalpy of the feedwater is 3396 kJ / kg, H. P1,T1 The value is 1044 kJ / kg. The design coal feed rate M when using the coal types shown in Table 1 under BMCR conditions is... coal，设 The design steam flow rate is 200 tons / hour, M. steam,设 The capacity is 1146 tons / hour, and the calorific value of the coal is Q. coal =22100kJ / kg.

[0098] Correction parameters

[0099] Table 1

[0100] project symbol unit numerical values Dry carbon α % (percentage by mass) 58 Dry-based hydrogen β % (percentage by mass) 4 Dry base oxygen γ % (percentage by mass) 8 Dry nitrogen δ % (percentage by mass) 1 Dry basis ash Ash % (percentage by mass) 30 calorific value of coal <![CDATA[Q coal ]]> kJ / kg 22100

[0101] The logic control method for reducing the load of a 300MW subcritical boiler from 100% BMCR to 20% BMCR is as follows:

[0102] If the target load BMCR of 20% in the pulverized coal boiler load reduction instruction is lower than 35% BMCR, it is considered an ultra-low load.

[0103] S1. First, reduce the boiler load of the pulverized coal boiler to 35% BMCR according to the load adjustment method for boilers operating under normal load. The specific process is as follows:

[0104] To maintain a constant superheater outlet temperature, determine the load reduction rate k1, where k1 is set to 1.5 tons / hour. 2 Equation 1 is used to calculate the steam evaporation rate; Equation 2 is used to calculate the coal feed rate of the pulverized coal boiler; and Equation 3 is used to calculate the total air volume of the pulverized coal boiler. In Equation 3, f... air 1120 Nm 3 / ton; calculate the primary air volume of the pulverized coal boiler using Equation 4, where the proportion of the primary air volume of the pulverized coal boiler to the total air volume of the pulverized coal boiler is η = 0.8; adjust the coal feed rate and primary air volume of the boiler in real time according to the calculation results to reduce the load of the pulverized coal boiler to the target load.

[0105] M steam = (1146-1146k1t) tons / hour Formula 1

[0106] 22100×M coal ×0.92=M steam ×[3396-1044]×1.51 Equation 2

[0107] F air =1.2 × 1120 × M coal Formula 3

[0108] F air-1 =0.8×F airFormula 4

[0109] During the period when the boiler load of the pulverized coal boiler is reduced to 35% BMCR according to the load adjustment method of the boiler when it is running under normal load, the mill operation mode is adjusted to further reduce the pulverized coal particles, so that the average particle size of the pulverized coal exiting the mill is about 75μm.

[0110] When the boiler load drops to 35% BMCR (i.e., M... steam =1146 × 0.35 = 401.1 tons / hour),

[0111] S1-1, Calculate the coal feed rate M of the boiler at this time. coal35％ The total air volume is 70 tons / hour, F air35％ 94080 Nm 3 / h, primary air volume F (air-1)35％ 75264 Nm 3 / h;

[0112] S1-2, Value of heat loss in gasifier The coal feed rate M of the gasifier is 3%, calculated using Equation 5. coal,1 It is 72.16 t / h;

[0113]

[0114] S1-3, the coal feed rate M of the gasifier. coal,1 Substitute equations 3 and 4 to calculate the primary air volume of the gasifier.

[0115] S1-4, Substitute the required coal feed rate of the gasifier into Equation 6 to calculate the inlet air volume of the gasifier:

[0116]

[0117] S1-5, Substitute the primary air volume and gasifier inlet air volume of the gasifier into Equation 7 to calculate the supplementary combustion air volume in the boiler combustion zone:

[0118]

[0119] S1-6, switch the coal powder feed from the boiler burner to the pusher flow gasifier, and increase the supplementary combustion air. Adjust the coal feed rate of the gasifier, the inlet air rate of the gasifier, and the supplementary combustion air rate of the boiler combustion zone according to the calculation results, and run for 25 minutes.

[0120] S2, calculate the minimum stable combustion temperature at the boiler burner using equations 8 and 9, where the specific heat value of air is c. p,air The specific heat value of pulverized coal is 1.07 kJ / (kg·K); the molar mass of air is 29 kg / kmol; the average specific heat value of pulverized coal is c. p,coalThe efficiency is 0.905 kJ / (kg·K), and the temperature of fresh pulverized coal and air entering the furnace is 80℃;

[0121]

[0122]

[0123]

[0124] The chemical equation for the pyrolysis of pulverized coal in the gasifier is shown in Equation 10:

[0125]

[0126] Syngas produced by pyrolysis in a gasifier was analyzed using a syngas component analyzer. The standard volume fractions of CO, CO2, CH4, H2, and N2 in the syngas were measured, with α2 = 0.12, α3 = 0.02, α4 = 0.001, α5 = 0.06, and α6 = 0.8.

[0127] The constant n is calculated using the nitrogen mass conservation formula 11.

[0128]

[0129]

[0130] n = 0.71

[0131] Substituting n = 0.71 into Equation 12-18, calculate the mass flow rate of each component in the synthesis gas:

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139] Substitute the calculation results from Equation 12-18 into Equation 19 to calculate the total flow rate of the syngas.

[0140]

[0141] tons / hour

[0142]

[0143] The calorific value of syngas, V, is calculated using Equation 20. H2 V CH4 V CO Measured by a gas analyzer, it is equal to α5, α4, and α2.

[0144]

[0145] Among them, the specific heat of air, c p,air The average specific heat value of the coal coke is 1.07 kJ / (kg·K); the average specific heat value of the coal coke is taken to be the same as that of the coal, which is 0.905 kJ / (kg·K); the temperature of the boiler supplementary combustion air is taken as 80℃.

[0146] The enthalpy of the syngas at its minimum stable combustion temperature is calculated using Equation 22. The enthalpy of each gas in the syngas at its minimum stable combustion temperature can be obtained from a gas enthalpy-temperature table, with units of kJ / Nm³. 3 ;

[0147]

[0148] Calculate the gasifier outlet temperature T2 using Equation 21:

[0149]

[0150]

[0151] Monitor the combustion zone temperature. If the temperature of the monitored combustion zone is higher than the minimum stable combustion temperature and the gasifier outlet temperature is greater than 1000℃, the boiler is operating stably. Keep the steam superheater outlet temperature constant and determine the load reduction rate k2. Calculate the steam evaporation rate using Equation 1. Calculate the coal feed rate of the gasifier using Equations 2 and 5. Calculate the primary air volume and gasifier inlet air volume of the gasifier using Equations 3, 4, and 6. Calculate the supplementary combustion air volume of the boiler combustion zone using Equation 7. Adjust the coal feed rate, gasifier inlet air volume, and supplementary combustion air volume of the boiler combustion zone in real time according to the calculation results until the boiler load is reduced to 20% BMCR.

[0152] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for stable combustion control of a push-flow gasifier coupled with a pulverized coal boiler system, characterized in that, The method includes the following steps: Determine whether the target load in the boiler load reduction instruction of the pulverized coal boiler belongs to the ultra-low load; wherein, when the target load is <35%BMCR, the target load is the ultra-low load; When the target load is not an ultra-low load, the load shall be adjusted in accordance with the load adjustment method for pulverized coal boilers operating under normal load. When the target load is an ultra-low load: S1. First, reduce the boiler load of the pulverized coal boiler to 35% BMCR according to the load adjustment method when the boiler is running under normal load. Then, switch the pulverized coal feed from the boiler burner to the pusher flow gasifier and increase the supplementary combustion air. Run for 10-30 minutes. S2, monitor the temperature in the combustion zone to determine whether the minimum stable combustion temperature and the gasifier outlet temperature meet the conditions for stable combustion in the pulverized coal boiler. When the temperature of the combustion zone is lower than the minimum stable combustion temperature, or the gasifier outlet temperature is less than 1000℃, it indicates that the boiler combustion is unstable. Increase the coal feed rate of the gasifier, keep the primary air volume of the gasifier constant, increase the inlet air volume of the gasifier, and reduce the supplementary combustion air volume of the boiler until the combustion is stable. When the temperature of the combustion zone is higher than the minimum stable combustion temperature and the gasifier outlet temperature is greater than 1000℃, it indicates that the boiler combustion is stable. Keep the steam superheater outlet temperature constant and adjust the coal feed rate of the gasifier, the air flow rate at the gasifier inlet, and the supplementary combustion air flow rate in the boiler combustion zone in real time until the pulverized coal boiler load is reduced to the target load. The method for adjusting the load according to the load adjustment method of the pulverized coal boiler under normal load includes: keeping the outlet temperature of the steam superheater constant, determining the load reduction rate k1, calculating the steam evaporation rate of the pulverized coal boiler using Formula 1 between the load reduction rate and the steam evaporation rate, calculating the coal feed rate of the pulverized coal boiler using Formula 2 between the steam evaporation rate and the coal feed rate, calculating the total air volume of the pulverized coal boiler using Formula 3 between the coal feed rate and the total air volume, calculating the primary air volume of the pulverized coal boiler using Formula 4 between the total air volume and the primary air volume, and adjusting the coal feed rate and the primary air volume of the pulverized coal boiler in real time according to the calculation results to reduce the load of the pulverized coal boiler to the target load. Formula 1 In Equation 1, k1 is the load reduction rate, ranging from 1.2 to 2.4, and h... -1 M steam Steam evaporation rate, tons per hour; M steam,0 The steam evaporation rate of the boiler upon receiving the instruction is tons per hour; t is time, hours. Formula 2 In Equation 2, Q coal M represents the calorific value of pulverized coal, in kcal / kg; coal θ is the coal feed rate (tons / hour); θ is the boiler efficiency; P is the steam pressure reference value (MPa); P1 is the feedwater inlet pressure (MPa); T is the steam temperature reference value (°C); T1 is the feedwater inlet temperature (°C); H P,T H represents the enthalpy of superheated steam, expressed in kJ / kg. P1,T1 enthalpy of water supply, kJ / kg; b1 correction factor; Formula 3 In Equation 3, F air Total air volume, Nm 3 / h; 1.2 is the excess air coefficient at the boiler furnace outlet, f air The amount of air required for the complete combustion of a unit mass of pulverized coal, in Nm³. 3 / ton; Formula 4 In Equation 4, F air-1 For primary air volume, Nm 3 / h; This represents the proportion of primary air volume to total air volume, with a value ranging from 0.7 to 0.

8. In step S1, switching the pulverized coal feed from the boiler burner to the push-flow gasifier and adding supplementary combustion air includes the following sub-steps: S1-1, Calculate the boiler coal feed rate M when the boiler load drops to 35% BMCR using equations 1 to 4. coal35% Total air volume F air35% and primary air volume F （air-1）35% ; S1-2, the coal feed rate M of the pulverized coal boiler coal35% Substitute the coal feed rate of the pulverized coal boiler and the coal feed rate of the gasifier into Equation 5 to calculate the coal feed rate of the gasifier. Formula 5 In Equation 5, M coal,1 φ represents the coal feed rate required for the gasifier, in tons per hour; φ represents the heat loss of the gasifier, ranging from 1% to 3%. S1-3, Substitute the coal feed rate of the gasifier into Equations 3 and 4 to calculate the primary air volume of the gasifier. Nm 3 / h: S1-4, Substitute the required coal feed rate of the gasifier into Equation 6 to calculate the inlet air volume of the gasifier: Formula 6 In Equation 6, The inlet air volume of the gasifier, Nm 3 / h; S1-5, Substitute the primary air volume and gasifier inlet air volume of the gasifier into Equation 7 to calculate the supplementary combustion air volume in the boiler combustion zone: Formula 7 In Equation 7, The amount of supplemental combustion air for the boiler combustion zone, Nm 3 / h; S1-6, adjust the coal feed rate of the gasifier, the air inlet rate of the gasifier, and the supplementary combustion air rate of the boiler combustion zone according to the calculation results, and run for 10-30 minutes; In S2, the coal feed rate M of the pulverized coal boiler is... coal35% and / or primary air volume F of pulverized coal boiler （air-1）35% Substituting into Equation 8, we can calculate the minimum stable combustion temperature at the boiler burner using Equation 9: Formula 8 In Equation 8, q min The volumetric heat load at the boiler burner outlet, kJ / m³ 3 V represents the furnace volume at the boiler burner outlet, in meters. 3 ; 0.08 represents the proportion of the total heat released during coal combustion at the boiler burner; Formula 9 In Equation 9, T feed,min Minimum stable ignition temperature, °C; T feed,0 The temperature at which fresh pulverized coal and air enter the boiler, in °C; c p,air is the specific heat value of air, kJ / (kg·K); c p,coal denoted as , which is the average specific heat value of pulverized coal, in kJ / (kg·K).

2. The control method according to claim 1, wherein, In S2, the gasifier outlet temperature is calculated using the following equations 10 to 21: The chemical equation for the pyrolysis of pulverized coal in the gasifier is shown in Equation 10: Formula 10 In Equation 10, Syngas produced by pyrolysis in a gasifier was analyzed and measured using a syngas component analyzer. The constant n is calculated using the nitrogen mass conservation formula 11, where the molar mass of coal is 27 g / mol and the molar mass of nitrogen is 28 g / mol. Formula 11 In Equation 12-18, the mass flow rate of each component in the synthesis gas is calculated: Formula 12 Formula 13 Formula 14 Formula 15 Formula 16 Formula 17 Formula 18 In Equations 11-18, α is the mass percentage of dry carbon in pulverized coal, β is the mass percentage of dry hydrogen in pulverized coal, γ is the mass percentage of dry oxygen in pulverized coal, and δ is the mass percentage of dry nitrogen in pulverized coal. Substitute the calculation results from Equation 12-18 into Equation 19 to calculate the total flow rate of the syngas. Formula 19 In Equation 19, F syngas Syngas flow rate, unit: Nm³ 3 / h; The calorific value of syngas is calculated using Equation 20. Formula 20 In Equation 20, V H2 It is the molar proportion of H2 in the dry-based syngas, V CH4 It is the molar proportion of CH4 in dry-based syngas, V CO It is the molar ratio of CO in dry-basis syngas, F H2O It is the flow rate of water vapor in the synthesis gas, in Nm³. 3 / h; Calculate the gasifier outlet temperature T2 using Equation 21: Formula 21 In Equation 21, ΔH syngas The enthalpy of the synthesis gas at its minimum stable combustion temperature is given in kJ / m³. 3 ; c p,char The average specific heat value of semi-coke is equal to that of coal, expressed in kJ / (kg·K); m char The mass of semi-coke is expressed in kg / h; c p,air Specific heat of hot air, kJ / (kg·K); T air,2 The temperature of the supplemental combustion air in the combustion zone of the pulverized coal boiler, in °C; F* air The amount of supplemental combustion air for the combustion zone of a pulverized coal boiler, Nm 3 / h; The enthalpy of syngas at its minimum stable combustion temperature is calculated using Equation 22. Equation 22; In Equation 22, The enthalpy values ​​of the individual gases in the synthesis gas are given in kJ / Nm³. 3 ; The flow rates of each gas in the synthesis gas are expressed in Nm³. 3 / h.

3. The control method according to claim 1, wherein, In S2, when the temperature of the monitored combustion zone is lower than the minimum stable combustion temperature, or the gasifier outlet temperature is less than 1000℃, the coal feed rate of the gasifier is increased by 3-8%; while keeping the primary air volume of the gasifier unchanged, the inlet air volume of the gasifier is increased by 15-30% until combustion is stable.

4. The control method according to claim 3, wherein, When the temperature in the combustion zone is lower than the minimum stable combustion temperature, or the gasifier outlet temperature is less than 1000℃, increase the coal feed rate of the gasifier by 4-6%; keep the primary air volume of the gasifier unchanged, and increase the inlet air volume of the gasifier by 20-25% until the combustion is stable.

5. The control method according to claim 1, wherein, In S2, the method for real-time adjustment of the coal feed rate of the gasifier, the inlet air rate of the gasifier, and the supplementary combustion air rate of the boiler combustion zone includes: Keep the steam superheater outlet temperature constant, determine the load reduction rate k2, calculate the steam evaporation rate using Equation 1, calculate the coal feed rate of the gasifier using Equations 2 and 5, calculate the primary air volume and gasifier inlet air volume of the gasifier using Equations 3, 4 and 6, and calculate the supplementary combustion air volume of the boiler combustion zone using Equation 7. Adjust the coal feed rate of the gasifier, the gasifier inlet air volume, and the supplementary combustion air volume of the boiler combustion zone in real time according to the calculation results until the boiler load is reduced to the target load.

6. The control method according to claim 1, wherein, The S1 also includes adjusting the operation mode of the coal mill during the process of reducing the boiler load of the pulverized coal boiler to 35% BMCR, so that the average particle size of the pulverized coal exiting the mill is 50-100μm.

Images